Antenna system compensating for polarization field rotation



E. DYKE April 17, 1956 ANTENNA SYSTEM COMPENSATING FOR POLARIZATION FIELD ROTATION I5 Sheets-Sheet 1 Filed Aug. 22, 1952 7 INVENTOR.

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April 17, 1956 E. DYKE ANTENNA SYSTEM COMPENSATING FOR POLARIZATION FIELD ROTATION Filed Aug. 22, 1952 3 Sheets-Sheet 2 INVENTOR.

w/fhyww/ E. DYKE April 17, 1956 ANTENNA SYSTEM COMFENSATING FOR POLARIZATION FIELD ROTATION I5 Sheets-Sheet 3 Filed Aug. 22, 1952 m m m m ANTENNA SYSTEM COWENSATING FOR POLARIZATION FIELD ROTATION Edwin Dyke, Brooktield, Ill., assignor to Motorola, Inc, Chicago, 111., a corporation of Illinois Application August 22, 1952, Serial No. 305,798

' 4 Claims. (Cl. 250- This invention relates generally to microwave relay systems and more particularly to antenna structures for such systems in which the plane of polarization of the wave is shifted to compensate for beam rotation resulting from the physical positioning of the various elements of the system.

Microwave relay systems are used in many applications to provide communication over relatively long distances by the use of a plurality of interconnecting links. In order to provide satisfactory communication over the enthe system itis necessary to provide eflicient transfer of energy over each of the individual links. For reasons of economy it is desired to hold the number of individual links to a minimum, and consideration must be given to the physical terrain over which the system extends in selecting the position for the various stations. For example, it is desirable to provide the stations at the highest possible elevation so that effective communications may be provided over relatively long distances in each link. Further, the stations must be positioned at accessible points to facilitate inspection and servicing of the system, and at points which are not unduly congested so that adequate space is available and interference is held to a minimum.

In view'of the above, the stations in a microwave system will not normally be arranged along a straight line. In addition to the physical conditions which might cause displacement of the paths from a straight line, it may be desired to provide communication or control functions at particular points, and for this reason it will be necessary to position the stations at these points which may be displaced from a straight line.

In order to provide a simple construction and one which may be standardized for use in various applications, the stations in the microwave system have been constructed with a fixed frame structure which supports not only the microwave units but also a housing for the unit, and a part of the antenna therefor. The antenna at the station directs the transmitted beam upward and may include a horn or a parabolic reflector or the like for forming the beam. This antenna also receives the beam and concentrates it as required. A reflector is provided above the station for changing the direction of the beam and may be a flat or curved reflector. To provide most efle'ctive communication, it is necessary that the antenna of each unit be positioned in line with the beam communicating with the unit. It is obvious that this relationship cannot be had when the line connecting the stations deviates from a straight line and the units and their antennas are in fixed position with respect to each other. Thei' deviation from the straight line position causes'a rotation of the beam, or a change in the plane of polarization thereof, which results in a loss in signal unless properly compensated for.

Another situation which causes rotation of the beam occurs when the terrain is such that the microwave unit itself may not conveniently be positioned directly below the reflector which directs the horizontal waves downwardly to the active antenna element adjacent the microwave unit (or upwardly therefrom). That is, to take advantage of a very high point, the antenna reflector itself may be positioned on a suitable tower on this high point. However, the terrain may be such that the microwave unit and its associated equipment cannot be provided directly on the peak and must be displaced therefrom. The angle of the flat reflector may be shifted so that the beam is directed to a position where the microwave equipment can be conveniently positioned. However, such deflection of the beam.may cause rotation of the plane of polarization thereof which results in a loss in signal level as previously described.

It is therefore, an object of the present invention to,

provide a microwave system which is effective to 00m.-

pensate for changes in the plane of polarization of the beam transmitted from one station to another.

A further object of this invention is to provide a microwave system made of standard units which are substantially identical for all stations and which with a minimum of alternate components may provide highly effective signal transfer between the stations of the system'under various conditions.

A feature of this invention is the provision of a microwave system including beam forming at the microwave units for directing waves vertically, and reflectors for converting these waves to horizontal waves, in which the horn providing coupling between the microwave unit and the parabolic reflector has a twisted section to cause a change of the plane of polarization of the beam trans- I mitted therethrough.

A further feature of this invention is the provision of a microwave system, having stations of a standard fixed construction with rigid wave guide couplings between the microwave units and the reflector wherein the couplings may have a twist therein for compensating for rotation of the beam resulting from displacement of the antenna with respect to the beam path. An optimum angle of twist of the coupling waveguide has been found to meet all situations within a satisfactory tolerance, by using units twisted in either a positive or a negative direction, and by using I such units either at only one or at both ends of any given link.

Another feature of this invention is the provision of a microwave system of the type wherein beams are transmitted upwardly and directed by a reflector to a substantially horizontal direction, in which a waveguide coupling section having a twisted portion for changing the polarization of the Waves transmitted therethrough is used to compensate for changes in polarization of the wave resulting from horizontal displacement of the microwave unit with respect to the flat reflector, out of line with the path of the beam to the flat reflector from the remote station.

Further objects, features and the attending advantages of the invention will be apparent from a consideration of the following description. when taken in connection with the accompanying drawings, in which:

Fig. 1 is a perspective view of a relay station including the antenna structure in accordance with the invention;

Fig. 2 illustrates schematically a microwave relay system in accordance with the invention;

Fig. 3 illustrates more in detail one station of the system of Fig. 2;

Fig. 4 illustrates a station in which the microwave unit is displaced with respect to the flat reflector;

Figs. 5, 6, 7 and 8 illustrate the structure of a straight waveguide horn; and,

Figs. 9, 10 and 11 illustrate the structure of a twisted waveguide horn.

Patented Apr. 17, 1956 ing vertically radiated waves "tohorizontal waves at the transmitter andfor converting the horizontal waves to vertical waves at the receiver. This system may be a relay system including a pair of terminal stations and at least oneintermediate station. The microwave'equiprnent'is of the type wherein the microwave units themselves are provided on the ground, or-in a suitable structure with other equipment-andincludes beam forming means at the top' thereof which direct waves upward and collect and concentrate waves coming downward. Positioned above the beamforming means are'the reflectors which convert the vertically directed waves into-horizontally directed waves and vice versa. The units are of a standardized construction wherein themicrowave equipment is provided on framework within-the housing which framework mayactually be a part'of thehousing'supporting structure and is therefore in afi'xedpositionwithin the housing. The microwave units are coupled to the beam formingfmeans, which may be parabolic reflectors, through rigid waveguidesections having horns which are positioned with respect tome-parabolic reflectors to illuminate the surface thereof. The beam forming means and couplings are also supported on the framework to provide a compact rigid construction. To compensate for rotation of the beam because of the fixed'position of the units of the system and-the angular direction of the beams thereto, rotation of the waves is provided in the wave guide coupling sections by providing a twistedportion in such sections. Sections having twists in opposite direction of a fixed amount which is of the order of 35 has been found to provide adequate compensation for all angles of'beam' rotation encountered. That is, small angles of deviation do notcause appreciable attenuation and may be tolerated, and largerangles may be taken care of by the use of twisted, sections at both ends of'a link in the relay system. The use of such twisted sections is alsoeitective to compensate for'changes in polariza tion from any other cause such as from the provision of the microwave unit at a position not directly under the fiat reflector.

Referring now to the drawings, in Fig. 1 there is illustrated a station such as is used in the microwave relay.

system, the station being of the type used at a relay station and including ,two microwave units; one for communication in each of the. links of which the relay station forms apart. It is pointed outthat the terminal station may be of substantially the same constructionexcept the terminal-station will require only a single microwave unit. The station includes a housing or building in which the two-microwave units 21 and22 are enclosed. The units 21 and 22 are supported by a framework 23.which may be mounted on the same foundation which supports the building 20 itself. Also the framework 23 may serve to help support a portion of the building 20 such as the center portion of the roof thereof.

Mounted above the roof of the building 20'are antennas 25' and 26 respectively, which are supported'on the frame structure 23. The antennas include parabolic reflectors 28 which are directed upwardly, and waveguide coupling section 29. The coupling sections are connected to the microwave units 21'and 22 and have hornportions positioned with respect to the parabolic reflectors 28 to illumihate the same, or to pick up waves received from the same. The waveguide sections 29 are rigid'metal conduits which are of minimum length for connection to the microwave units 21 and 22. These sections have the advantage of simplicity of structure and provide eflicient operation because the characteristics of the rigid'sections can be precisely controlled. For converting the vertical waves communicating with the parabolic reflectors 28 to horizontal waves, flat reflectors 30 are providedlwhich are supported on a tower. structure3l extendingabove the building '29. This tower structure may be of any suitable configurationbut it may be necessary that the towers be relatively high so that the path between the flat reflectors of units at the ends of each relay link will be in line of sight and willclear intervening objects.

In Fig. 2 there is illustrated a microwave relay system including the terminal station 35, relay station 36, relay station 37 and terminal station 38. As will be apparent from Fig. 2 the beam path between the various stations of the system deviates from-a straight line. This may be necessary because it is desirable that the stations 35, 36,

37 and 38 each be at a relatively high point so that the distance between the stations over which effective communication may be provided will be relatively great. Further, it may be desirable. to communicate into the system from station 36 and/or station 37. For example,-the microwave relay system may follow a pipeline and the stations 36 and 37 may be at stations on the pipeline at which it is desired to control or observe the characteristics of the pipeline.

In order to use the standardized structure as illustrated in Fig. 1 it is not possible to position the microwave units 40 and 41 at station 36 for example in line with the beam paths which communicate with these units. This may be because the beams of the two links of which.

the unit 36is a part are not at an angle of with respect to each other, or may also be because it is desired to orient the unit 36in a particular direction because of various conditions of the terrain which might be encountered. In this connection it is to be pointed out that although the terminal stations 35 and 38 which include only a single unit can theoretically be oriented in a manner desired to provide the required alignment with the beam communicating with these stations, it may be desired because of physical condition adjacent the stations 35 and 38' to position the housings in a particular direction. That is, the position of other buildings or other equipment connected with the terminal stations may make. it preferable to position the building housing.

these stations ina particular direction.

It is therefore apparent that it may not be possible to position the units at the opposite ends of a microwave link in the optimum position with respect to the direction of the beam therebetween. For example, the unit 41 of station 36 and the unit 42 of station 37 may both be controlled in position by other factors and therefore when using standard fixed structure as illustrated in Fig. l, the communication therebetween may be greatly affectedby the rotation of the beam in its path through theair between the parabolic reflector of the units. 41 and 42. This wave from the. parabolic reflectors as previously Y stated is coupled to the microwave unit through waveguide section 29 (see Fig. 3). The coupling waveguide section has a rectangular horn 43 at the end which controls the polarization of the signals transmitted or received. By providing a twist in the waveguide section adjacent the horn the polarization of the wave applied thereby to the the waveguide coupling portion 46 connected to the microwave unit. In Figs. 9 to 11 inclusive there is illustrated a waveguide coupling unit wherein the born 47 is,

rotated with respect to the coupling portion 48 connected to the microwave unit by the use of a twisted section 49.

It is to be pointed out that in considering the total amount of rotation, the rotation at both ends of the link must be considered. The rotation of the beam.may: in.

some instances: be such that the rotation at'the two ends compensate for each other and no corrective measures are required. Onthe other hand, the angle ofrotationzmay be quitev substantial; and may cause substantial; attenuate tion in thereceivedsignal. It has been found that when the total angle of rotation is less than 25, the loss in signal is less than one decibel, and this is of such a minor nature that no correction need be provided. However, when the angle is increased to more than 25 the loss becomes much greater and correction thereof is highly important. It has been found that the use of a twist of 35 makes it possible to correct for all angles with very small errors. This is because it is possible to correct at both ends of the link so that the correction may be as much as 70. In the case of a maximum rotation of 90, this would result in an error of only 20", which as previously stated results in a loss of less than one decibel.

It is necessary to provide coupling sections having rotations in both directions because the rotation of the angle may be in either direction. It will be apparent that when horns are provided having twists of 35 in both directions and that by using either a twist at only one end of the link or at both ends of the link the resulting error can never be more than 20. This therefore provides a relatively simple structural solution to the problem of rotation of the beam in a microwave system.

Although the situation previously described accounts for the principal cause of rotation of the beam in a microwave system, there are other instances in which rotation of the beam occurs and in which the use of a twisted waveguide coupling element will be eifective to increase the signal response. One such example is illustrated in Fig. 4. As previously stated there are some instances in which it is impossible to locate the microwave unit, housing, etc. at the very highest peak available and yet it is desired to take advantage of the height of the peak. In such instances it may be possible to mount the flat reflector on a support or tower at the highest peak, and then direct the beam to one side to a location where the microwave unit may be positioned. This is illustrated in Fig. 4 in which the tower 50 supporting the flat reflector 51 is at one position and the building 52 housing the microwave unit is at another position. The beam therefore is deflected by the flat reflector to the parabolic reflector 53 on top of the house 52. The beam reaching the reflector 53, however, is rotated by the reflecting process and it may be necessary to provide a waveguide coupling unit 29 in which the horn 54 is rotated with respect to the connection thereof to the microwave unit. The same considerations as to angles apply as previously stated, and it is therefore possible to make corrections so that the signal attenuation is a minimum by the use of sections twisted through one angle, approximately 35 with the twist being in either direction to compensate for either direction of rotation of the plane of polarization.

It will be apparent from the above that a system is provided for compensating for rotation of the beam in a microwave system. This permits the use of standard units at the relay and terminal stations and gives freedom as to the positioning of these units without causing a resulting attenuation in the signal. Further, the waveguide coupling is accomplished by a minimum number of alternate structures with the coupling retaining the advantage of being a rigid member so that the characteristics thereof can be accurately determined. The twisted horn strucnires when used in the proper combination are effective to correct for all angles with a maximum loss of one decibel.

The use of a rigid wave guide is much to be preferred over the use of a flexible coupling for several reasons. First, the flexible couplings require clamps to support the same, and supporting means for the horn at the end thereof to fix the position of the same. The flexible couplings must also be longer than a rigid coupling as disclosed herein and this aflects the loading of the system. The flexible guide structures are relatively expensive and the cost is further increased because of the additional length required and the supporting structure required for the guide itself and for the horn. The operation of the twisted rigid sections is superior to that of the flexible couplings because the bending of the flexible couplings 1. A radio relay system operating in the microwave range including at least two stations forming a communication link, said stations providing a microwave unit having an antenna structure at each end of each link, each of said antenna structures including an upwardly positioned beam directing. means, rigid waveguide means coupled to the microwave unit and to said beam directing means, and reflector means positioned above said beam directing means for converting the vertical wave to a horizontal wave, said reflector means at said stations at the ends of said link being positioned to direct Waves toward each other, at least one of said reflector means being positioned with respect to the associated antenna structure to cause a rotation of the angle of polarization of the wave reflected thereby, and at least one of said rigid waveguide means of said antenna structures at the ends of said link including a twisted section for compensating for rotation in the angle of polarization of waves transmitted over said link.

2. A radio relay system operating in the microwave range including at least two stations forming a communication link, each of said stations having an antenna ineluding an upwardly positioned parabolic reflector, rigid wave guide means having a downwardly extending rectangular horn portion for coupling waves to said parabolic reflector, and a substantially flat reflector positioned above said parabolic reflector for converting the beam from said parabolic reflector to a horizontal beam, said parabolic reflector of at least one of said antennas being displaced horizontally from said flat reflector with respect to the direction of the horizontal beam to said flat reflector, said wave guide means of at least one of said stations including a twisted section for rotating the plane of polarization of the wave transmitted therethrough to compensate for the rotation of the plane of polarization resulting from the displacement of said flat reflector.

3. A radio relay system for operation in the microwave range including a station having a microwave unit mounted in a fixed position, an antenna connected to said unit for operation with a vertical microwave beam, and

reflector means positioned above the antenna for converting the vertical beam to a horizontal beam, said reflector means being displaced horizontally from the antenna with respect to the direction of the horizontal beam, said antenna including upwardly positioned beam directing means, and rigid Wave guide means adapted to be connected to said microwave unit and including a portion for coupling waves to said beam directing means, said wave guide means including a twisted section for rotating the plane of polarization of the wave transmitted therethrough to compensate for the rotation of the plane of polarization resulting from the displacement of the reflector means.

4. A radio relay system operating in the microwave range including a pair of terminal stations and at least one relay station, each of said terminal stations including a microwave unit having an antenna, each of said relay stations including a pair of microwave units in fixed position with respect to each other and each unit having an antenna, each of said antennas including upwardly positioned beam directing means, rigid waveguide means coupled to the microwave unit and to the beam directing means, and reflector means positioned above the beam directing means for converting a vertical wave to a horiz.0I-1tal:wave,.said reflector means at each station being positioned to direct waves toward said refiectormeans-at the next station to form a microwave relay link, at'least oneof saidreflector.means ofzone relay station being positioned with respectto the associatedantenna-to'cause rotation of the angle of polarization of the wave reflected thereby an'd atleast one of said rigid waveguide, means of-said antennas at the ends-of thevlink including said one. reflector means having, a twisted. section for compensating forrotation .in the angle of polarization of waves transmitted over said link.

References Cited in the file of this patent UNITED STATES PATENTS.

1,927,394- Darbord et al Sept: 19,- 1933 OTHER REFERENCES Indirect Microwave Relay System by R. R. Wakeman, Tele-Tech Magazine, September 1948, pages 42, 43, 106.

News Pictures, FM-TV Magazine, January 1950, page 17. 

